This thoroughly researched study of Michigan's PBB scare (1973-75) marshals the farmers, corporations, scientists, and government officials involved in a controversy whose ramifications may not be known for years. It is the ""new large-scale public health menace,"" says Detroit News science writer Edwin Chen--""the silent, invisible chemical time bomb."" The basic Story has been told before (in Ted and Rick Halbert's personal account, and on TV's ""Lou Grant""): a chemical company manufacturing the fire-retardant PBB and a cattle-feed additive inadvertently sent PBB to the Michigan Farm Bureau. It was mixed with feed, cattle fell ill (humans too), milk production dropped. The subsequent investigation involved scientists with conflicting theories; official cover-ups; and economic realities (farmers--not compensated for contaminated cattle--sold as many as 100,000 ""heavily contaminated"" cows; Michigan's Farm Bureau knowingly sold contaminated feed). Scientists predict a ""sharp rise"" in the state's cancer rates in 15-20 years (""It is simply not known if PBB is a cancer-causing chemical,"" but preliminary evidence is positive), and residents of at least 13 other states may have been contaminated by Michigan exports, including swine flu vaccine. More than 4,500 Michigan residents are now part of a continuing health study, and there is also an ongoing program for testing potentially-exposed cattle. Chen's detailed account is sometimes hard to follow, and an extraneous story of Rick Halbert helping a cow in labor makes for a confusing opening. Still, a valuable resource, worthy of follow-up in years ahead.